refactor(iroha_config): Immutable configuration

[aoyako]

Refactors config structures to be externally immutable, as suggested in #4282.

Now, instead of directly accessing the config struct field, two approaches are adopted:

1. To read the config field, getters are used (currently auto-generated). It is possible to override with a custom logic in the future.
2. To change the config field, the config must be rebuilt from a builder (currently auto-generated). It is possible to add validation when the config builder actually generates a config.

The exception for mutability is log_level for the logger. Since there are many level switching, I believe it must not impact other configurations.

Pros:

• Configuration is immutable and keeps invariants when parameters are interdependent.

Cons

• Configs are inconvenient to use, i.e., now require separate builders.
• Deconstruction is not possible, requiring frequent clone()s.

At this moment no validation or custom logic for getters/setters is implemented.
Possible options include, but are not limited to:

• [suggestion] Fallible setters for configuration parameters #3528

[0x009922]

With all respect to the work being done, I am doubting whether this refactor is really that valuable...